Calling All Car Gurus!

Rod Zapa, my trustworthy 1998 Mazda Protege, has been having some very frustrating idle problems lately. I will spare no detail in hopes that one of my more car-familiar readers might be able to find a clue.

1998 Mazda Protege, Manual. 123k miles.

Frequently during neutral deceleration (with or without the break), the tachometer will dip aggressively to its occasional demise. The car will either idle precariously at 100-200rpm, shudder and return to ~650 rpm, or stall. Once the car is warmed up (> ~6 minutes of driving), the problem does not occur.

This only happens during deceleration. Once the car settles at a stop light or stop sign, the idle bounces back to a somewhat stable 750rpm (the idle still seems to quaver just slightly.) This is really weird to me. As soon as the car relaxes backwards at a stop the idle pops back to normal.

This occurs regardless of whether the clutch is in, or out.

Weather (wet vs dry) does not seem to impact the problem much, though the problem is less pronounced when it’s cold outside.

Car Diagnosis So Far:
I have had the following car components fixed within the last 6 months.

1. timing belt (unrelated?)
2. breaks and calipers (unrelated)
3. muffler system (unrelated?)
4. spark plugs and wires
5. distributor cap and rotor
6. O2 sensor front
7. O2 sensor rear
8. Fuel Filter

My mechanic reports that excessive carbon build up in the throttle body has been cleaned.

My mechanic also reports that he found no leak in the vacuum system.

The belts currently screech like a banshee for the first 60 seconds after I turn the car on.

The engine light has tripped with O2 sensor faults on two of the three stalls (it hasn’t tripped since the rear O2 sensor was replaced).

Car Gurus of, any ideas?

7 thoughts on “Calling All Car Gurus!

  • 10/5/2010 at 11:01 am

    Ben linked me, Mike.

    You have a bad idle control valve- absolutely classic symptoms. A quick Google search shows they ain’t cheap. Find a pick and pull (junkyard) and grab one there.

    If you had the throttle body cleaned of carbon while on the car, they likely blew carbon into the ICV. It might be something that can be cleaned, but usually the solvents do more harm than good.

    Good luck!

    • 10/5/2010 at 11:03 am

      Thanks for stopping by, and I greatly appreciate your recommendation!

    • 10/9/2010 at 4:54 pm

      I vote this one – if your idle air controller is near shot, that would do it.

  • 10/5/2010 at 1:54 pm

    Get an older car. My 1990 Buick Regal 2 Door coupe has no problems at all. You could probably trade a high school kid for his car and a couple Gorditas.

    • 10/5/2010 at 1:55 pm

      Ladies and Gentlemen? This is wisdom right here.

      This is wisdom.


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